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A reply to the discussion by T. Knudsen of the paper “studies of alkali-silica reaction. Part 7. Modeling of expansion”
CEMENT and CONCRETE RESEARCH. Vol. 21, p. 199, 1991. Printedin the USA. 0008-8846-91. $3.00+00. Copyright (c) 1991 Pergamon Press pl¢.
^ REPLY t o The D i s c u s s i o n By T . K n u d s e n o f t h e Paper "STUDIES ALKALI-SILICA REACTION. PART 7.MODELING OF EXPANSION."
OF
S.Chatterji D e p a r t m e n t of C i v i l E n g i n e e r i n g Kanazawa U n i v e r s i t y , J a p a n .
This discussion i s s y m p t o m a t i c of t h e p r e s e n t s t a t e of cement r e s e a r c h in that some of t h e r e s e a r c h e r s seem t o have f o r g o t t e n parts of t h e b a s i c science; i n t h i s c a s e t h e c o n f u s i o n i s a b o u t t h e m e a n i n g of t h e c r i t i c a l points. All modeling equations for real-life materials are valid within some w e l l d e f i n e d l i m i t s ; a t and b e y o n d t h o s e l i m i t s t h e m o d e l i n g e q u a t i o n s b r e a k down. These breakdown p o i n t s a r e known as c r i t i c a l p o i n t s . Take f o r instance the t h e r m a l e x p a n s i o n of a m e t a l . The t e m p e r a t u r e - e x p a n s i o n r e l a t i o n s h i p c o u l d be modeled by an e q u a t i o n ; b u t t h i s e q u a t i o n w i l l breakdown a t a critical t e m p e r a t u r e g e n e r a l l y known as t h e m e l t i n g t e m p e r a t u r e . The t h e r m a l e x p a n s i o n of t h e r e l e v a n t m e t a l a t or v e r y n e a r t h e m e l t i n g p o i n t c o u l d n o t be c a l c u l a t e d by p u t t i n g t h e m e l t i n g t e m p e r a t u r e i n t h e m o d e l i n g e q u a t i o n ; a l t h o u g h t h e b a s i c mechanism of t h e r m a l e x p a n s i o n n a m e l y k i n e t i c m o t i o n of t h e atoms r e m a i n s o p e r a t i v e . A s i m i l a r s i t u a t i o n o c c u r s i n t h e m o d e l i n g of t h e d e g r e e of h y d r a t i o n - t i m e r e l a t i o n s h i p of a cement p a s t e when i t shows an i n d u c t i o n p e r i o d ; t h e m o d e l i n g e q u a t i o n b r e a k s down n e a r t h e u p p e r l i m i t of t h e i n d u c t i o n p e r i o d as D r . K n u d s e n ' s own work so c l e a r l y shows. I t i s , o f c o u r s e , a l e g i t i m a t e o p e r a t i o n to i n q u i r e or s p e c u l a t e on t h e r e a s o n s f o r t h e breakdown i n a p a r t i c u l a r c a s e . However e x p e r i m e n t s d e s i g n e d t o find t h e m o d e l i n g e q u a t i o n will n o t , i n g e n e r a l , g i v e any i n f o r m a t i o n on t h e r e a s o n s of t h e breakdown ; f o r t h a t o t h e r t y p e of e x p e r i m e n t s would have t o be c a r r i e d o u t . I n t h i s c o n t e x t my r e c e n t c a l c u l a t i o n s , c a r r i e d out for other p u r p o s e and u s i n g o t h e r f o r m a l i s m s , seem t o i n d i c a t e t h a t a t the critical points the penetration of a l k a l i i o n s i n t h e reactive grains stops or virtually stops i.e. no a l k a l i - s i l i c a reaction o c c u r s and t h e reaction c h a n g e s o v e r t o t h e slow l i m e - s i l i c a r e a c t i o n . T h i s i s c o n s i s t e n t w i t h our e a r l i e r o b s e r v a t i o n s t h a t m o r t a r b a r s made w i t h Nymolle sand when s t o r e d i n a 0.5N sodium c h l o r i d e s o l u t i o n show no s i g n of e x p a n s i o n or a l k a l i - s i l i c a r e a c t i o n . W i t h o u t any a l k a l i - s i l i c a r e a c t i o n no e x p a n s i o n i s e x p e c t e d . As r e g a r d s t h e r o l e of c a l c i u m h y d r o x i d e i n a l k a l i - s i l i c a expansion I suggest t h a t D r . K n u d s e n r e a d s D i a m o n d ' s k e y - n o t e p a p e r i n t h e P r o c e e d i n g s of t h e 8 t h I n t e r n a t i o n a l C o n f e r e n c e on A l k a l i - A g g r e g a t e R e a c t i o n h e l d i n Kyoto i n 1989. I n t h a t p a p e r Diamond n o t o n l y a c k n o w l e d g e d t h e r o l e of c a l c i u m h y d r o x i d e in t h e e x p a n s i o n b u t a l s o added some f u r t h e r d a t a on t h a t p o i n t .
*CCR 20(2), 285-290 (1990). 199
^ REPLY t o The D i s c u s s i o n By T . K n u d s e n o f t h e Paper "STUDIES ALKALI-SILICA REACTION. PART 7.MODELING OF EXPANSION."
OF
S.Chatterji D e p a r t m e n t of C i v i l E n g i n e e r i n g Kanazawa U n i v e r s i t y , J a p a n .
This discussion i s s y m p t o m a t i c of t h e p r e s e n t s t a t e of cement r e s e a r c h in that some of t h e r e s e a r c h e r s seem t o have f o r g o t t e n parts of t h e b a s i c science; i n t h i s c a s e t h e c o n f u s i o n i s a b o u t t h e m e a n i n g of t h e c r i t i c a l points. All modeling equations for real-life materials are valid within some w e l l d e f i n e d l i m i t s ; a t and b e y o n d t h o s e l i m i t s t h e m o d e l i n g e q u a t i o n s b r e a k down. These breakdown p o i n t s a r e known as c r i t i c a l p o i n t s . Take f o r instance the t h e r m a l e x p a n s i o n of a m e t a l . The t e m p e r a t u r e - e x p a n s i o n r e l a t i o n s h i p c o u l d be modeled by an e q u a t i o n ; b u t t h i s e q u a t i o n w i l l breakdown a t a critical t e m p e r a t u r e g e n e r a l l y known as t h e m e l t i n g t e m p e r a t u r e . The t h e r m a l e x p a n s i o n of t h e r e l e v a n t m e t a l a t or v e r y n e a r t h e m e l t i n g p o i n t c o u l d n o t be c a l c u l a t e d by p u t t i n g t h e m e l t i n g t e m p e r a t u r e i n t h e m o d e l i n g e q u a t i o n ; a l t h o u g h t h e b a s i c mechanism of t h e r m a l e x p a n s i o n n a m e l y k i n e t i c m o t i o n of t h e atoms r e m a i n s o p e r a t i v e . A s i m i l a r s i t u a t i o n o c c u r s i n t h e m o d e l i n g of t h e d e g r e e of h y d r a t i o n - t i m e r e l a t i o n s h i p of a cement p a s t e when i t shows an i n d u c t i o n p e r i o d ; t h e m o d e l i n g e q u a t i o n b r e a k s down n e a r t h e u p p e r l i m i t of t h e i n d u c t i o n p e r i o d as D r . K n u d s e n ' s own work so c l e a r l y shows. I t i s , o f c o u r s e , a l e g i t i m a t e o p e r a t i o n to i n q u i r e or s p e c u l a t e on t h e r e a s o n s f o r t h e breakdown i n a p a r t i c u l a r c a s e . However e x p e r i m e n t s d e s i g n e d t o find t h e m o d e l i n g e q u a t i o n will n o t , i n g e n e r a l , g i v e any i n f o r m a t i o n on t h e r e a s o n s of t h e breakdown ; f o r t h a t o t h e r t y p e of e x p e r i m e n t s would have t o be c a r r i e d o u t . I n t h i s c o n t e x t my r e c e n t c a l c u l a t i o n s , c a r r i e d out for other p u r p o s e and u s i n g o t h e r f o r m a l i s m s , seem t o i n d i c a t e t h a t a t the critical points the penetration of a l k a l i i o n s i n t h e reactive grains stops or virtually stops i.e. no a l k a l i - s i l i c a reaction o c c u r s and t h e reaction c h a n g e s o v e r t o t h e slow l i m e - s i l i c a r e a c t i o n . T h i s i s c o n s i s t e n t w i t h our e a r l i e r o b s e r v a t i o n s t h a t m o r t a r b a r s made w i t h Nymolle sand when s t o r e d i n a 0.5N sodium c h l o r i d e s o l u t i o n show no s i g n of e x p a n s i o n or a l k a l i - s i l i c a r e a c t i o n . W i t h o u t any a l k a l i - s i l i c a r e a c t i o n no e x p a n s i o n i s e x p e c t e d . As r e g a r d s t h e r o l e of c a l c i u m h y d r o x i d e i n a l k a l i - s i l i c a expansion I suggest t h a t D r . K n u d s e n r e a d s D i a m o n d ' s k e y - n o t e p a p e r i n t h e P r o c e e d i n g s of t h e 8 t h I n t e r n a t i o n a l C o n f e r e n c e on A l k a l i - A g g r e g a t e R e a c t i o n h e l d i n Kyoto i n 1989. I n t h a t p a p e r Diamond n o t o n l y a c k n o w l e d g e d t h e r o l e of c a l c i u m h y d r o x i d e in t h e e x p a n s i o n b u t a l s o added some f u r t h e r d a t a on t h a t p o i n t .
*CCR 20(2), 285-290 (1990). 199